This week has started out with a few close calls for things in orbit. On Monday, what is believed to be an asteroid the size of a house safely flew by Earth without incident. The asteroid, designated 2011 MD, flew by at only 7,600 miles above Earth which is closer than most communications satellites. Now it seems the astronauts aboard the International Space Station (ISS) dealt with their own close call on Tuesday.

The six-member crew aboard the ISS were forced to take refuge in the Russian Soyuz TMA-21 after it was discovered that space junk was making its way toward the space station. According to reports, the astronauts entered the safety of the Soyuz capsule at 7:50am in the event the crew had to make a quick escape due to a catastrophic impact. Luckily for the crew, the debris avoided the station, though narrowly, at a distance of about 820 feet. Astronauts spent a total of 20 minutes in their “lifeboat” before receiving the all-clear.

Normally, when the ISS is detected to be in the path of space junk the orbiter is maneuvered out of the way. Such a maneuver took place in April of this year to avoid a previously cataloged piece of space debris. Unfortunately, this time around engineers didn’t have that luxury since the debris wasn’t discovered until it was too late. In fact, scientists are currently unsure what the debris was and have yet to report its size.

Space debris can include natural and man-made particles which pose a safety risk to equipment and personnel in orbit. Even small pieces of debris pose a risk due to the fact they can travel at speeds of up to 17,500 mph. It is believed that there are currently 500,000 pieces of debris in orbit which are the size of a marble or larger. Where the true danger comes from is in the smaller pieces of debris which could number in the millions and can’t be tracked. Such debris includes paint flecks which have caused enough damage to the windows of the Space Shuttle that they have had to be replaced.